1. Field of the Invention
The present invention relates to an ultrasonic imaging system. The system is comprised of an ultrasonic imaging catheter (an ultrasonic catheter) and a diagnostic imaging apparatus for employing information obtained by the catheter for diagnostic purposes, and more particularly to an ultrasonic catheter for being inserted into a blood vessel in a living body to obtain information such as an ultrasonic image. The diagnostic imaging apparatus functions to obtain an intravascular image from information obtained by an ultrasonic catheter.
2. Description of the Related Art
Ultrasonic diagnostic imaging apparatus for use in body cavities generally have an ultrasonic catheter for scanning a body vessel such as a blood vessel or a vessel.
FIG. 1 of the accompanying drawings shows a structure of a distal end portion 1 of such a general ultrasonic catheter. As shown in FIG. 1, the ultrasonic catheter has a catheter tube 2 housing an imaging core therein. The distal end portion 1 is guided by a guide wire (not shown) and inserted into a blood vessel in a living body. The distal end portion 1 has a guide wire lumen tube 3 which has a lumen 5 defined therethrough to receive the guide wire. The guide wire extends through the lumen 5 and guides the ultrasonic catheter in the blood vessel. An X-ray marker 4 made of gold, platinum, or the like is mounted on the tip end of the guide wire lumen 3. The X-ray marker 4 gives a visual indication as to the location of the ultrasonic catheter 1 in the living body in an X-ray radioscopic image.
The ultrasonic catheter also has a priming through hole 6 defined in the distal end portion thereof for removing air from the catheter tube 2 when the catheter tube 2 is filled up with a normal saline solution. The catheter tube 2 houses therein an X-ray marker 7 in the form of a metal coil. The X-ray marker 7 also serves as a stiffener for preventing the ultrasonic catheter from being bent.
A transducer housing 8 disposed in the catheter tube 2 accommodates an ultrasonic transducer 9 therein. A coil 10 is mounted on the tip end of the transducer housing 8 for stabilizing the rotation of the transducer housing 8 when a drive shaft 11 coupled to the transducer housing 8 is rotated by a motor (not shown). The drive shaft 11 is connected to the motor and houses signal lines therein. A coil is wound around the outer surface of the drive shaft 11.
While the drive shaft 11 is being rotated by the motor, the ultrasonic transducer 9 emits and receives ultrasonic waves reflected from the inner wall of the blood vessel in all directions (360° for generating a tomographic image of the blood vessel.
Japanese patent publication No. Hei 7-38852 discloses an ultrasonic probe for sending and receiving ultrasonic waves to acquire a tomographic image of the blood vessel, and introducing the blood from the blood vessel and measuring the temperature of the introduced blood with a temperature sensor. That disclosed ultrasonic probe can detect the temperature of the blood, as well as a tomographic image of the blood vessel like the ultrasonic catheter shown in FIG. 1, for diagnostic purposes.
The distal end portion 1 of the ultrasonic catheter shown in FIG. 1 has only the ultrasonic transducer 9 and is unable to detect the temperature in the blood vessel in a particular location in the living body.
The ultrasonic probe disclosed in Japanese patent publication No. Hei 7-38852 suggests that an ultrasonic tomographic image is displayed on a display unit such as a display monitor or the like. However, it fails to disclose anything about how the temperature information of the blood that is measured by the temperature sensor is used, and about how the temperature information is visually presented. It can only be guessed from the disclosed ultrasonic probe that a numerical value of the temperature information may be displayed together with the ultrasonic tomographic image.
Furthermore, the above two conventional devices suffer the following disadvantages: An intravascular ultrasonic device will be described by way of example. The intravascular ultrasonic device is used to observe the nature of a blood vessel or a blood vessel lumen or the form of an arterial sclerosis in a constricted area which is responsible for a cardiac infarction or the like, and to select an appropriate therapy. The intravascular ultrasonic device is also used to perform a chronological observation of how the arterial sclerosis develops, whether the blood vessel is constricted again, or whether the diameter of the blood vessel changes. The observation is merely the acquisition of information about a plaque that has already been formed. The above analysis applies to the above two conventional devices.
Attempts have been made in recent years to use the intravascular ultrasonic device to measure the intravascular temperature or the temperature of an arteriosclerotic plaque to predict the possibility of an arterial sclerosis. It has been reported that when an arteriosclerotic plaque, though not clearly confirmed by an image, is formed in an arterial coronaria, the intravascular temperature is 0.11±0.11° C. higher than the normal intravascular temperature when the patient is suffering stable angina, 0.68±0.35° C. higher than the normal intravascular temperature when the patient is suffering unstable angina, and 1.47±0.69° C. higher than the normal intravascular temperature when the patient is suffering acute myocardial infarction.
It has also been reported that the temperature of a plaque in a carotid artery, or the temperature in a carotid artery if there is a danger of the formation of a plaque, is 0.4 to 2.2° C. higher than the normal intravascular temperature.
An intravascular ultrasonic diagnostic imaging apparatus has a catheter with an ultrasonic transducer incorporated therein. The catheter is inserted into a blood vessel, and the ultrasonic transducer in the catheter is rotated to perform radial scanning on the blood vessel. Based on reflected ultrasonic waves, the intravascular ultrasonic diagnostic imaging apparatus displays a tomographic image of the blood vessel on a display monitor.
An intravascular temperature may be measured by a thermodilution catheter though the thermodilution catheter is originally used for other purpose.
The above two conventional devices need to produce an ultrasonic intravascular tomographic image and measure a temperature separately. Therefore it cannot accurately identify where each of the temperature data is measured in the blood vessel or where there is the plaque because the location where the temperature is measured cannot be specified.